You need to design a solution that can join a single time dimension to both fact tables

You are designing a data warehouse with two fact tables. The first table contains sales per
month and the second table contains orders per day.
Referential integrity must be enforced declaratively.
You need to design a solution that can join a single time dimension to both fact tables.
What should you do?

A.
Join the two fact tables.

B.
Merge the fact tables.

C.
Create a time dimension that can join to both fact tables at their respective granularity.

D.
Create a surrogate key for the time dimension.

Explanation:
http://msdn.microsoft.com/en-us/library/ms174537.aspx
http://technet.microsoft.com/en-us/library/ms174832.aspx
http://msdn.microsoft.com/en-us/library/ms174884.aspx
http://decipherinfosys.wordpress.com/2007/02/01/surrogate-keys-vs-natural-keys-forprimary-key/
http://www.agiledata.org/essays/keys.html
http://www.databasejournal.com/features/mssql/article.php/3922066/SQL-Server-NaturalKey-Verses-Surrogate-Key.htm
http://www.jamesserra.com/archive/2012/01/surrogate-keys/